1. Field of the Invention
The invention relates generally to semiconductor processing equipment and more particularly to devices and methods for etching one side of a semiconductor wafer while protecting the other side of the wafer from reactive gases.
2. Description of the Prior Art
Silicon nitride and other films are commonly applied to semiconductor wafers during process fabrication. Such films after they have served their purpose are removed so that the next process step may be done. For example, silicon wafers can be selectively patterned with oxide structures by coating the wafer with silicon nitride, applying a photoresist to the silicon nitride, and patterning the photoresist so that holes in the silicon nitride can be opened up. The remaining nitride is then used as a mask for subsequent oxidation of the exposed areas of silicon. After the oxide is grown the remaining silicon nitride mask is removed or cleaned.
In conventional processes, the frontside of the wafer must be cleaned while upright and then turned over to clean the backside. Extra steps are needed to protect the structures being fabricated on the frontside while the backside is being stripped of silicon nitride. Prior art systems strip the silicon nitride or other film from the frontside of the wafer and then deposit a photoresist to protect the frontside. The wafer is then turned over, and the silicon nitride is removed, e.g., by a reactive gas flow. The wafer is then ashed to remove the photoresist on the frontside.
Such prior art methods are labor intensive and not very conducive to high volume production with cluster processing equipment, such as the UNO marketed by Gasonics, Inc. (San Jose, Calif.). What is needed are devices and methods that can eliminate the wafer turning and the extra steps of depositing and ashing films to protect the wafer frontside from cleaning operations directed at the wafer backside.